1. Field of the Invention
This invention relates to the use of microorganisms or elaboration products thereof for the suppression of sprouting in stored potatoes.
2. Description of the Prior Art
In the North America alone, the total annual potato production is 393 million cwt. In excess of 70% of that crop is stored, representing a $1.4 billion investment. Typically, tubers are harvested, allowed to suberize (i.e. allow the "skin" or periderm layer to toughen) at warm temperature .about.15.degree. C. for about 10 days, then gradually cooled down to the storage temperature of about 7-13.degree. C. For the first 1-2 months after harvest, the tubers remain dormant and exhibit little inclination to sprout. However, after this period, the tendency for the tubers to sprout results in numerous deleterious effects. These include a loss of fresh weight, the conversion of starch to sugars, and a decrease in the quality and appearance of tubers sold fresh. Sprouts and the surrounding tissue also contain elevated levels of toxic glycoalkaloids, which are destroyed by cooking. Because of the adverse effects caused by sprouting, sprout control is required for the 54% of potato crop used for process potatoes.
Low storage temperatures around 3.degree. C. are an effective sprout deterrent, but process potato quality is lost at very low temperatures due to the high rate of accumulation of soluble sugars. Thus, because of processing demands, over 54% of the annual potato harvest must be stored at 7.degree. to 13.degree. C., a temperature range above that needed for ideal sprout control ("Design and Managment of Storages for Bulk, Fall-crop Irish Potatoes", ASAE Standards, St. Joseph, Mich., 1990). If storage temperatures exceeding 3.degree. C. are required, chemical sprout inhibitors must be applied to control sprouting. Sprout inhibitors can be applied during the growing season, after storage, or as potatoes are moved into storage. Two chemicals are used in the United States. Maleic hydrazide, a systemic compound, must be applied to the plant foliage before harvest and is not amenable to application on stored potatoes (Yada et al., "The Effect of Maleic Hydrazide (Potassium Salt) on Potato Yield, Sugar Content and Chip Color of Kennebec and Norchip Cultivars", Am. Potato J., 68:705-709, 1991). Moreover, the timing of this foliar application is critical to its success. Consequently, CIPC (Chlorpropham; 1-methylethyl-3-chlorophenylcarbamate) is the most widely used sprout inhibitor world-wide. It can be applied as a dust, granule, spray or dip as potatoes enter storage, or most effectively as a fog during storage, but suitable ventilation systems are required (Orr et al., "Design and Performance of a Test Facility for Evaluating Potato Sprout Inhibitors", Transactions of the ASAE, 37(6):1899-1905, 1994; Leach, "Quality of Stored Potatoes Improved by Chemical Treatment", Am. Potato J., 55:155-159, 1978; Duncan et al., "Methods for Controlling Sprouting in Potatoes", Aspects of Applied Biology, 33:189-196, 1992). CIPC is a mitotic inhibitor known to have an inhibitory effect on wound healing, and for this reason its application is often delayed until after suberization in order to prevent storage rots from gaining access (Duncan et al., "Methods for Controlling Sprouting in Potatoes", Aspects of Applied Biology, 33:189-196, 1992). Although irradiation processes inhibit sprouting, they generally have a detrimental effect on the chemical composition of the tuber and lack practicality for application (Leszczynski et al., "Effect of Gamma Irradiation on Potato Quality and Subsequent Production of Chips", Pol. J. Food Nutr. Sci., 1/42 (No.3):61-69, 1992; Hayashi et al., "Identification of Irradiated Potatoes by Electrical Measurements", J. Food Irradiat., Japan, 26:66-72, 1991).
The potato industry has become very dependent on CIPC as the most efficient sprout inhibitor with fewest detrimental side-effects on process potato quality. CIPC is the only synthetic chemical presently registered as a sprout inhibitor for post-harvest application to stored potatoes in the United States. However, CIPC is known to be among the three agrichemicals found in highest concentrations in the diet of the average American (Gartrell et al., "Pesticides Selected Elements, and Other Chemicals in Adult Total Diet Samples, October 1980-March 1982", J. Assoc. Off. Anal. Chem., 69:146-159, 1986), and it comprises over 90% of the total synthetic chemical residues found in U.S. potatoes (Gunderson, J. "FDA Total Diet Study, April 1982-April 1984, Dietary Intakes of Pesticides, Selected Elements, and Other Chemicals", Assoc. Off. Anal. Chem., 71:1200-1209, 1988). Because of its persistence in the environment and potato tissue, concerns about its toxicity have been under review by the Environmental Protection Agency. CIPC is a derivative of ethylurethane, a well-known carcinogen, and it is not known whether CIPC, once ingested, is converted back to this parent compound (Mondy et al., "Effect of Storage Time, Temperature, and Cooking On Isopropyl N-(3-chlorophenol) Carbamate Levels in Potatoes", J. Agric. Food Chem., 40:197-199, 1992). Because of its vulnerable position, the potato industry is in search of alternative agents for sprout control. Natural products less persistent in the environment are among the alternatives being studied in various laboratories (Orr et al., "Design and Performance of a Test Facility for Evaluating Potato Sprout Inhibitors", Transactions of the ASAE, 37(6):1899-1905, 1994; Vaughn et al., "Volatile Monoterpenes Inhibit Potato Tuber Sprouting", Am. Potato J., 68:821-831, 1991; Vaughn et al., "Antifungal Activity of Natural Compounds Against Thiabendazole-resistant Fusarium Sambucinum Strains", J. Agric. Food Chem., 42:200-203, 1994).
Vaughn et al., U.S. Pat. No. 5,139,562, and Vaughn et al., U.S. Pat. No. 5,129,951, disclosed that the oxygenated monoterpenes cineole, fenchone and menthol, as well as several aromatic aldehydes and alcohols, including thymol, hydrocinnamaldehyde, cuminaldehyde, salicylaldehyde, cinnamaldehyde, and benzaldehyde, may be advantageously used to inhibit potato tuber sprouting, fresh weight loss, rotting, and fungal growth. Vaughn et al., U.S. Pat. No. 5,129,951, also reported that the aromatic acid, benzoic acid, did not inhibit tuber sprouting.
Lulai et al., U.S. Pat. No. 5,436,226, disclose the use of various jasmonate compounds for controlling sprouting in tubers and for improving their processing qualities.
Lulai et al., U.S. Pat. No. 5,635,452, disclose a method for inhibiting sprouting of potato tubers comprising exposing potato tubers to an aromatic acid, including anisic acid, coumaric acid, gallic acid and mixtures thereof.
In studies of allelopathy, it is well established that microorganisms play an important role in plant growth regulation by producing bioactive products (Putman et al., The Science of Allelopthy, John Wiley & Sons, New York, N.Y., 1986; Inderjit et al., "Allelopathy Organisms, Processes, and Applications", ACS Symposium Series 58, American Chemical Society, Washington, D.C., 1995). Such products may either stimulate or inhibit plant growth. Natural products derived from microbes have been sought and commercialized as herbicides or plant growth regulators for the protection of agricultural crops. Unlike their synthetic derivatives, such natural products are attractive pest control agents because their persistence in the environment is limited by biological and/or chemical degradation, hence minimizing any risk of ecological disturbance.